Polyethylene terephthalate, cellulose triacetate, polystyrene, polycarbonate and like polymers have been prevailingly used as photographic support materials due to their desirable characteristics such as a high degree of transparency, and flexibility. However, difficulties arise when using these polymers as support materials, for such supports have hydrophobic surfaces and photographic layers to be coated on the supports (e.g., a light-sensitive silver halide emulsion layer, an interlayer, a filter layer, etc.) are made up of protective colloids containing gelatin as a main component. Therefore, it is difficult to firmly adhere a photographic layer to the surface of the support. In an attempt to obtain stronger adhesion, various treatments have been developed for activating the surfaces of hydrophobic supports. Examples of types of surface activating treatments include chemical treatments, mechanical treatments, corona discharge treatments, flame treatments, ultraviolet ray treatments, high frequency wave treatments, glow discharge treatments, activated plasma treatments, laser treatments, mixed acid treatments, and ozone oxidation treatments. Two general techniques have been used to increase adhesiveness between a hydrophobic support and a photographic layer. According to one technique, a photographic emulsion is coated directly on the surface of a hydrophobic support treated by one or more of the above-described surface treatments. According to another technique, after a hydrophobic support has been treated by one or more of the above-described surface treatments, a subbing layer is provided on the support and then a photographic emulsion is coated on the subbing layer. This technique is described in U.S. Pat. Nos. 2,698,241, 2,764,520, 2,864,755, 3,462,335 and 3,475,193, British Pat. Nos. 788,365, 804,005 and 891,469.
Of the two techniques, the latter is more effective and prevails now. All of the surface treatments are intended to create polar groups to some degree. Some treatments also increase cross-linking density at the surface of a support which is hydrophobic by nature. This increases the affinity for polar groups of a certain component contained in a subbing solution, as well as increasing the fastness at the interface formed between the support and the subbing layer by adhesion. In addition, various different subbing layers have been developed. For instance, a double layer process in which a layer which can adhere well to a support is first provided on the support (hereinafter the first subbing layer). On top of the first layer is coated a hydrophilic resin layer which can strongly adhere to a photographic layer (hereinafter the second subbing layer). In a single layer process a resin having both hydrophobic and hydrophilic groups is coated on a support.
Both processes have been closely studied. A number of resins have been examined to determine their usefulness as the first subbing layer in the double layer process. For example, copolymers prepared using as starting materials monomers selected from a group comprising of vinyl chloride, vinylidene chloride, butadiene, methacrylic acid, acrylic acid, itaconic acid and maleic anhydride; polyethylene imine; epoxy resin; grafted gelatin; and nitrocellulose. Gelatins have been principally tested for their usefulness as a second subbing layer. These processes have been shown to possess satisfactory adhesion power to a conventional gelatin silver halide photographic emulsions. However, recently there has been a tendency to decrease the silver contents in silver halide photographic light-sensitive materials in order to conserve resources. In order to prevent the lowering in image density with a low silver content, it is necessary to swell photographic layers largely during development-processing. This requires a reduction in the contents of hardeners in the photographic layers. When the hardener content is decreased, a new problem develops involving the adhesion strength between a photographic layer and the second subbing layer. The adhesion becomes insufficient, particularly at the development-processing stage. Subbing solutions for the first subbing layer may contain an aldehyde series, an active vinyl series, an active halogen series and like series hardeners. In many cases, such a hardener is incorporated into the first subbing layer in a large amount. This creates strong adhesion between the first subbing layer and the plastic film support. However, the increased hardener content in the first subbing layer causes a reduction in adhesion strength between the second subbing layer and photographic layer. In addition, the subbing layer containing a large amount of hardener exerts undesirable influences upon photographic characteristic, such as lowering image density.